Depth-selective conversion electron

DCEMS, depth selective conversion electron Mossbauer spectroscopy (Liljequist and Ismail, 1985)... 

Conversion electron Mossbauer spectroscopy (CEMS) measurements with back scattering geometry have the merit that spectra can be obtained from a sample with much less isotope content compared with transmission measurements. Another merit is that a sample, deposited on a thick substrate, could be measured, and that because of the limited escape depth of the conversion electrons, depth-selective surface studies are possible. The CEMS technique was found to be best applicable to specimens of 10-100 pg Au cm, i.e., about two orders of magnitudes thinner than required for measurements in transmission mode [443]. This way (1) very thin films of gold alloys, as well as laser- and in beam-modified surfaces in the submicrometers range of depth [443], and (2) metallic gold precipitates in implanted MgO crystals [444] were investigated. 

Since the conversion electrons emitted from the sample surface have different energies depending on the depth they were generated in, it is theoretically possible to record Mdssbauer spectra characteristic of selected surface layers of the sample at different depths. Geometric effects and the relatively wide energy spectrum of the various kinds of emitted electrons (K- and L-conversion, Auger, etc.) result in rather poor depth resolution. 

There is a concept of the depth selectivity by analyzing the energy of the conversion electrons emerging from the surface. The spectra are accumulated separately for the electrons of different energies, assuming that the energy loss of electrons clearly correlates with the depth at which they originate [36]. 

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